<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script>
        var str1 = "好好学习";
        var str2 = '好好学习';

        var str3 = new String("ss");

        var a = str1.length;

        var str4 = '   abc     ';
        //去除空格
        console.log(1 + str4.trim() + 1);



    </script>
</head>

<body>

</body>

</html>